It is common practice to protect identification cards and other documents, including driver's licenses, student identification cards, security system identification documents, and the like, by sealing such documents into covers of thin, tough, transparent plastic film. One of the best known protective films for this purpose is a laminate that includes an outer film of hard, tough, abrasion resistant biaxially oriented thermoset polyester resin coated with an inner layer of a thermoplastic adhesive resin activatable by heat and pressure. The resin for the outer film is usually polyethylene terephthalate; the most frequently used adhesive resin is polyethylene. To complete a protective cover on an identification card or like document, the document is usually placed between two sheets of the laminating film and then passed through a laminating press in which heat and pressure are applied to activate the thermoplastic adhesive, bonding the film to the surfaces of the document; around the edges, the two sheets of laminating film may bond directly to each other.
A laminated assembly of this kind provides excellent protection for the identification document. The outer film of thermoset polyester withstands a great deal of abuse. It remains very hard, tough, and abrasion-resistant with little change due to aging; the transparency of the film is also little changed with age. The protective cover also makes it quite difficult to alter the identification card.
Identification documents protected by laminated covers of thermoset polyester film have not been suitable for a number of applications. Thus, the thermoset polyester film on the outer surface of a document assembly of this kind cannot be effectively embossed after lamination; indeed, it is extremely difficult to emboss at any time because the heat, pressure, and time requirements for effective embossure are excessive. Furthermore, it is difficult to obtain effective adherence between any supplementary external film and the surface of the hard polyester film. For example, in those applications in which it is desirable to provide a magnetizable strip on the protected document for the recording of an identification number or other security information, it becomes necessary to locate the magnetizable strip in the interior of the laminated document assembly. An inside location for a magnetizable strip is not desirable because the protective laminate increases the spacing between the strip and any recording or reading transducer. Moreover, with a protected document assembly of this construction, the document cannot be signed or otherwise validated by the user after lamination because the thermoset polyester film on the outer surface does not accept ordinary inks; the ink wipes off.
A laminating film that retains the basic advantages of the conventional sealed thermoset polyester cover and that also allows for surface embossure, for signature reception on the exterior of the sealed document cover, and for mounting of an external magnetic strip on the cover is described in the copending United States patent application of H. M. Drower and M. Minkus, Ser. No. 385,460 filed June 7, 1982 issued as U.S. Pat. No. 4,456,639 on June 26, 1984. That laminating film incorporates an external layer of an unoriented embossable thermoplastic polyester resin, extrusion coated onto the oriented thermoset polyester resin film. Covers made with this laminate have the proven protection characteristics of conventional sealed covers with the added features of embossability and acceptability of externally mounted magnetic strips and signature strips.
In the utilization of the Drower et al three layer laminate (thermoplastic polyester, thermoset polyester, and adhesive resin) precise control of laminating parameters, particularly the laminating temperature, must be maintained. Excessive temperatures may soften the exterior layer of thermoplastic polyester resin, and fouling of the laminating press may result. Thus, that laminate is not readily adaptable to processing with some commercial laminating presses, particularly the small, inexpensive presses frequently used for individual identification documents. Moreover, the thermoset polyester resin film used as the central layer in that laminate is unnecessary in some applications, particularly when maximum durability are not critically important; in such applications, a sealed cover of thermoplastic polyester resin would afford adequate protection with potentially appreciable cost reduction, particularly if the heat-activatable adhesive resin is also eliminated.